There has been one duration of electrical stimulus (0.2 milliseconds) that has been used in the majority of studies and in clinical practice. With this duration of stimulation, the vast majority of cases show a unilateral motor response of the lower limbs during the TCEST. Studies on the stimulation of peripheral nerves (nerves in the arms and legs) have shown that an electrical stimulus with a longer duration is able to stimulate nerves which are farther away. Since nerves in the epidural space are similar in composition to peripheral nerves, the investigators expect to see a higher rate of bilateral response with the longer duration of stimulus. The investigators also hope to show that this bilateral response is predictive of a better functioning epidural.